1. Field of the Invention
The present invention is in the field of curable compositions and more particularly to curable coating compositions which are useful as clear coats in color-plus-clear coating applications. The invention also relates to a process for preparing color-plus-clear coated articles and to the coated articles themselves.
2. Brief Description of the Prior Art
Color-plus-clear coating systems involving the application of a colored or pigmented base coat to a substrate followed by the application of a transparent or clear top coat to the base coat are becoming increasingly popular as original finishes for automobiles. The color-plus-clear systems have outstanding gloss and distinctness of image, and the clear coat is particularly important for these properties. Two-pack clear coat compositions comprising polyols such as polyester polyols, polyurethane polyols and acrylic polyols and polyisocyanate curing agents give outstanding gloss and distinctness of image. However, the polyisocyanates are difficult to handle being sensitive to moisture and require cumbersome safety precautions because of their toxicity.
The patent applications mentioned under "Cross-Reference to Related Applications" disclose crosslinkable coating compositions which avoid the problems of polyisocyanate curing agents. The crosslinkable coating compositions are based on polyepoxides and polyacid curing agents. Although these coatings can be formulated to produce coatings with excellent adhesion, gloss and distinctness of image (i.e., ability to reflect images in a clear, well-defined manner), these compositions sometimes need an auxiliary crosslinking agent to provide optimum solvent resistance.
A good auxiliary crosslinking agent is an aminoplast, however, the aminoplast sometimes adversely affects the appearance of the resultant coating in that holes or bubbles known as popping often develop in the surface of the coating during curing. It has been found that the incorporation of a relatively long carbon chain monocarboxylic acid into the coating formulation helps to overcome the popping problem and provide for better appearance in the coating. It has also been found that the long carbon chain monocarboxylic acid also helps to overcome the popping problems caused by certain volatile solvents in the coating composition.